Instrument for laying out arcs of circles.



Patented Mar. 24, 1914 2 SHEETSWSHEET 1.

APPLIATION FILED JULY 18, 1913.

C. W. ROEHRIG.

INSTRUMENT FOR LAYING OUT ARCS 0F GTRGLES.

' APPLICATION FILED .TULY18, 1913. 1,091,246.

Patented Mar. 24, 1914 2 SHEBTS-SHBET 2.

k w I v 7255' Wip ITED STATES PATENT OFFICE.

CHARLES. WILLIAM ROEI-IRIG', 0F ST. LOUIS, MISSOURI.

INSTRUMENT FOR IIAYING OUT ARCS 0F CIRCLES.

Specification of Letters Patent.

Patented Mar. 24, 1914.

Application filed July 18, 1913. Serial No. 779,670.

ful Improvement in Instruments for Laying e Out Arcs of Circles, of which the following is a specification.

This invention relates to instruments used by draftsmen, engineers and others for laying out arcs of circles of large radius, more particularly arcs of circles having their centers of curvature beyond reach.

The object of the invention is an instruinent which may be used for laying out and drawing arcs of circles varying in size up to an indefinitely large radius and .corre-` spondingly small degree of curvature.

Another object of the invention is an instrument with which an are of a circle vcan be drawn without reference to its center, which may be inaccessible.

A further object is an instrument which may be used for plotting any segmental curve, comprising one or more circular ares, provided any two points on each arc, or the locus of the tangent at each end of each segnient is known and can be plotted.

Other objects and possibilities of adaptation of the invention will be evident to those skilled in the art from the description of the device illustrated in the accompanying drawings, and-in what the invention consists is particularly pointed out in the appendedclaims.

In the drawings, in which the same referk ence characters designate like parts in the several views,-Figure 1 is a plan view of the middle portion and part of the right hand half of the instrument in the position in which it is set up or adjusted for use; Fig. 2 is a view in elevation of the saine,

looking at the near side in Fig. 1; Fig. 8 is a` plan view of the left hand portion of the instrument in the position in which it is set up;

for use; Fig. l is a lengthwise sectional view of the portion shown in Fig. 3, taken on the center line of the instrument; Figs. 5 and 6 are transverse sectional views taken on the` Fig. 8; Fig. 8 is an end view of the telescop` ing angle clamp; and Fig. 9 is a perspective view of the adjustable anchor pin clamp.

The invention consists essentially of a long straight flexible rod and vmeans for clamping it between its ends to a base plate. The rod is made of a strip of uniformly tempered steel, or other homogeneous elast-ic material, and is of uniform cross section from end to end. Such a flexible rod, if freely supported at two points along its length, and sub# jected to a uniform bending movement between said points, will be defiected between said two points from-a straightline to an arc of a circle.

In the device illustrated in the drawings, the flexible rod 10 is removably secured at its iniddle by means of a clamp bolt 11 and thumb nut 12 to an arm 13 on an adjustable cross slide 14 slidably mounted in a transverse groove extending across the upper surface of the beain 15 at its middle point. A block 16 having a groove 17 extending across its under face mating with the transverse groove in the beainis secured to the latter at its middle. The mating grooves in the beam and block form a slide-way for the cross slide. A scale 18 reading to inches and tenths of an inch is marked on the top of the cross slide. The middle portion of the block is slotted in from the edge adjacent to the arm of the cross slide and the sides 20 of the opening thus formed are beveled. A fixed index pointer 21 is attached to the block and projects partly across the opening between the beveled walls 20 in position to coperate with the scale 18. The Zero of the scale 18 coincides with the fixed index pointer 21 when the outer face of the rod is in the vertical plane of the farther edge 19 of the beam. The'cross slide is adjusted by means of a screw 22 attached to its inner end and threaded through a nut 23 rotatably secured to the near edge of the block 16 by means of a disk 2/1 screwed thereto bearing against a shoulder 25 on the inner end of the nut. The body of the nut is cylindrical, and is circumferentially marked with five equally spaced division lines, bearing the numbers 1 to 5 respectively. The respective marks designated 1 to 4: are also marked 6 to 9 respectively. A Zero line 26 is marked on the disk 24 in position to cooperate with the division lines on the nut. The screw 22 is Vthreaded with twenty threads per inch, and

accordingly, each turn of the nut 23 through one division on its periphery moves the cross slide one one hundreth of an inch.

The two ends of the flexible rod are secured in adjustable angle clamps 27 by means of thumb screws 28. Each angle clamp is composed of two channel shaped guides telescoped one within the other. The tixed guide 30 is pivoted at its end nearer the middle point of the rod to the slidable clamp 31 by means of the vertical anchor pin 32. The anchor pin is xed to the under side oi' the guide 30, and its lower end engages the jaws 33 on the end of the clamp near the farther edge 190i' thebeam. For convenience in setting up the instrument the anchor pin is detachably secured in the jaws 33 by means of the removable pin 34. The axis oit' the anchor pin is thereby located at vthe intersection of the beveled edge 35 of Vthe clamp and the rear edge 19 of the beam.

This point is at the intersection of the edge 19 of the beam and the outside edge of the rod 10 at the point where the curve joins the tangent.

The front and back edges of the beam are parallel and are marked on top with scales y 3G graduated in inches, and tenths, having the Zero point at the middle line of the beam and reading up toward each end of the beam. The rod is marked with a similar scale Y37. The clamps 31 are provided with thumb screws 38 whereby they may be secured at any desired distance along the beam from its middle line, the beveled edge 35 serving as a means for locating them with respect to the scales 36.

The movable guides 29 of the adjustable angle clamps are slidable within the fixed guides 30 at their ends nearer to the middle ot' the rod. Each guide is pivoted at its nearer end by means of a king pin 39 to a bracket 40 mounted on a shoe 41 slidably arranged on the beam between its end and the anchor pin clamp. The axis of the king pin is parallel to the anchor pin, and about three tenths of an inch inside of the rear edge 19 of the beam. The end of the movable guide farther from the middle of the rod is mounted to swing about the king pin 39 through an angle of about thirty-live degrees from a position nearly parallel to thev edges of the beam, and is secured in adjusted position by a thumb nut 42 and clamp bolt 43 having a flange 44 at its lower end which slides in a slotted segment 45 fixed to the shoe 41. The slotted segment is marked with a scale 46 graduated in degrees and half degrees, and reading from 0 to 35 degrees. An index pointer 47, attached to the end of the guide 29, swings above the scale whereby the guide may be set at any desired angle.

The ends of the beam are supported in blocks 48 provided with end knobs 49 for manipulating the instrument. The instrument is supported at the middle on the bottom block 50. The tops of the blocks 48 and the tops of the projections 51 on the middle block 1G lie in a plane slightly above the top edge of the rod 10, whereby the rod is supported slightly above the surface of the paper when the instrument is turned over in order to draw in the curve for which it has been set.

In order to use the instrument for plotting a curve it is necessary to know, in addition to the radius (or degree of curvature) one-hali'l the chord length, the middle ordinate (2'. e. the perpendicular distance :trom the chord to the middle point of the arc) and the deflection angle (i. c. the angle between the chord and the tangent to the end of the arc) for an arc of any convenient length. In addition thereto, it is desirable to know the length of the arc. Accordingly, a table is prepared giving this necessary data for a selected number of arcs varying in radius (or degre of curvature) and covering the range through which it is desired to use the instrument.

A convenient table for use with the instrument shown in the drawings is one giving arcs varying from about seven and a half inches in length for those of small radius up to about twenty-one inches in length for those of large radius.

The following specimen will serve to illustrate a convenient form of table:

Degree 0f Middle 1 lema] n 7 Y g eiection length iillq .ordlnate pt chord angle in of are iu 100 it. 1n inches. m inches. degrees. inches.

.' 1.67 72T() 24 3U' 7.91 .G l. 67 7.71 24 30 7.95 .S 1. 03 7.63 24 00' 7.87 .0 1.64 7.73 24 U0' 7.95

The instrument is set up for use as follows: The cross slide 13 is projected to the distance corresponding to the middle ordinate of the desired curve, which is obtained from the third column of the table. Next.l the two anchor pin clamps 31 are cach set at the distance from the middle line of the beam corresponding to the one half chord length, which is obtained from the fourth column of the table. Following the clamping of the anchor pin clamps, the shoes 41 are slid lengthwise along the beam until the index pointers 47 attached to the movable guides 29 point to the angular division on each scale 4G corresponding to the deliection angle, which is obtained from the litth column of the table. The ends of the rod 10 may then be inserted in the clamps 27, and the division marks thereon corresponding to one half the length of the arc should be adjusted to line up with the near edges of the clamp screws 2S (i. e. at the intersection points of the arc and chord). The half arc length is obtained from the sixth column of the table. The clamp screws are tightened and the instrument is turned upside down, thereby bringing the rod close to the surface upon which the arc is to be described.

In Figs. 1 and 2 the instrument is shown set up for laying out a curve of 18 inches radius, and in Figs. 3 and 4l it is shown set up for laying out a curve of 80 inches radius.

The instrument, when set up for any desired curve, may be used precisely in the same way that an ordinary templet conforming to that curve is used. Other ways of using the instrument will occur to those havin need to plot circular arcs.

It 1s evident that the mechanical constructions illust-rated in the drawings may be modified or replaced by equivalent constructions without departing from my invention, and I do not restrict my invention to the embodiment thereof shown and described.

What I claim as my invention is as follows:

1. An instrument for laying out arcs of circles comprising a flexible rod and means for clamping it at two points on each of two lines tangent to a circle of the desired size.

2. An instrument for laying out curved lines comprising a beam, a flexible rod, and means for clamping said rod to said beam toward its ends, said clamping means being mounted for angular adjustment with respect to the longitudinal axis of said beam.

3. An instrument for laying out curved lines comprising a beam, a flexible rod, and means for clamping said rod to said beam toward its ends, said clamping means being adjustable lengthwise along said beam and mounted for angular adjustment with respect to the longitudinal axis of said beam.

4l. In an instrument for laying out curved lines, a flexible rod and means for holding the same comprising an extensible guide for securing the rod therein, an anchor post at one end of said extensible guide, and a sector at the other end thereof, said guide having adjustable means for clamping it to said sector.

5. In an instrument for laying out curved lines, a flexible rod and means for holding the same comprising an extensible guide,

clamps at each end of said extensible guide for securing the rod therein, an anchor post at one end of said extensible guide, a movable king pin secured to said extensible guide intermediate its ends, and a sector at the other end thereof, said sector and king pin being connected for simultaneous movement and s'aid guide having adjustable means for clamping it to said sector.

6. In an instrument for laying out curved lines, a flexible rod and means for holding the end of said rod comprising a guide, clamps at each end of said guide for securing the rod therein, an anchor post at one end of said guide, and a sector at the other end thereof, said guide having adjustable means for clamping it to said sector.

7 An instrument for plotting curved lines comprising a base, a flexible rod clamped above said base, and end rests projecting above said base, the tops of said end rests extending slightly above the top edge of said flexible rod, said rests having means whereby said instrument may be turned over and the rod will be supported parallel to the surface upon which the curve is to be described with a slight space between it and said sur face.

8. A n instrument for plotting curved lines comprising a base, a flexible rod clamped above said base, and end rests projecting above said base and having their tops parallel thereto, said rests being provided with axially arranged knobs whereby said instru ment may be turned over and the rod will be supported parallel to the surface upon which the curve is to be described.

9. An instrument for laying out arcs of circles comprising means for determining and fixing the length of said arc, means for determining and fixing the end points of the chord subtending said arc, means for determining and fixing the end point of the middle ordinate to said arc from said chord,

and means-,for determining and fixing the deflection angles of the tangente at the ends of said arc.

Signed at St. Louis, Missouri, this 15th day of July, 1913.

CHARLES WILLIAM ROEI-IRIG. Witnesses:

BAXTER L. BROWN, AMAsA M. I-IoLcoMBE.

Copiezof this patent may be obtained for ve cents each, by addressing the Commissioner of Patenti,

Washington, D. C. 

